The production of discs used in the magnetic disc drive industry begins with the creation of a substrate with a hard smooth surface that magnetic material can be deposited onto. A hard smooth surface may be formed by coating a relatively soft material such as an aluminum disc with a hard material such as nickel. The hard material is polished to a smooth finish, and magnetic material is then deposited onto the hard material surface of the disc. Several methods for depositing magnetic material onto the disc surface can be used; for example, electrodeposition and sputtering are two well known methods.
After polishing, the workpieces are then typically cleaned prior to the surface deposition of magnetic material. If the surface of the workpiece is contaminated with debris from the polishing process or elsewhere, the adherence of the magnetic material to the surface of the workpiece will be imperfect, and "blisters" of missing magnetic material will form on the surface of the workpiece. These "blisters" create areas on the workpiece that are incapable of storing information. Similarly, in optical disc manufacturing, debris on the surface of the workpiece may cause voids in information storage. In semiconductor wafer manufacturing, debris may attach to the surface of the workpiece, causing defects on the surface of the workpiece. These defects can cause electrical shorts or other problems within the microelectronic structures on the workpiece. Accordingly, it is often important to clean the workpieces to remove debris from the corresponding surfaces.
Contact scrubbing with sponge-like material is one method used to remove debris from the surface of the workpiece. A typical prior art cleaning device used for contact scrubbing of workpieces is described in U.S. Pat. No. 5,311,634, issued May 17, 1994 to Andros, the entire content of which is hereby incorporated by reference. A typical prior art cleaning device is also schematically shown in FIG. 1. Referring to FIG. 1, cleaning device 10 includes sponge-like material 12 and a core 14. Cleaning device 10 has two substantially coplanar surfaces 16 and 18. Sponge-like material 12 is "grown" over core 14 and seals with itself at an outer edge 20 of core 14. Sponge-like material 12 may be made of a variety of resilient materials, including poly vinyl alcohol and urethanes. Core 14 has an aperture 22 at its center to allow a rotatable shaft 24 to be inserted therein. Core 14 may also have two keyways 26(a) and 26(b) formed within aperture 22 and configured to receive a key 30 on rotatable shaft 24. Key 30 and keyways 26(a) and 26(b) enable rotatable shaft 24 and cleaning devices 10 to rotate as a single unit.
Core 14 is often made of a substantially rigid material. Thus, as a force is applied by key 30 to keyway 26(a) or 26(b), core 14 may become deformed, allowing cleaning device 10 to slip on rotatable shaft 24. In addition, because core 14 is somewhat flexible, as more cleaning devices 10 are attached to rotatable shaft 24, the pressure exerted on the workpiece from surfaces 16 and 18 changes from the center to the edge of rotatable shaft 24. For example, for a rotatable shaft 24 containing fifty-two cleaning devices 10, the cumulative displacement of cleaning devices 10 in the direction substantially parallel to the axis of rotatable shaft 24 may be 0.5". The changing pressure exerted by cleaning device 10 on the workpieces may yield unpredictable cleaning of the workpieces.
When multiple cleaning devices 10 are placed on rotatable shaft 24, a number of spacers 32 are often interposed between adjacent cleaning devices 10 to ensure substantially identical spacing between all cleaning devices 10. Unfortunately, attaching spacers 32 to rotatable shaft 24 is time consuming and labor intensive. Spacers 32 also tend to wear and become contaminated, causing nonuniform spacing between cleaning devices 10. Such nonuniform spacing between cleaning elements 10 may cause unpredictable workpiece cleaning.
In addition to the above shortcomings of the prior art, cleaning devices 10 are difficult to correctly align on rotatable shaft 24. As shown in FIG. 1, keyways 26(a) and 26(b) enable cleaning device 10 to be mounted onto rotatable shaft 24 in four different ways. In particular, cleaning device 10 could be mounted with its front surface 16 forward with keyway 26(a) in contact with key 30; with front surface 16 forward with keyway 26(b) in contact with key 30; with rear surface 18 forward with keyway 26(a) in contact with key 30; or with rear surface 18 forward with keyway 26(b) in contact with key 30. The multiple keyway system is typically employed in an attempt to obtain consistent spacing between cleaning devices 10 and consistent pressure exerted between cleaning devices 10 and the associated workpieces. For consistent spacing, cleaning devices 10 are often mounted onto rotatable shaft 24 such that front surface 16 of one cleaning device 10 faces the rear surface 18 of another cleaning device 10. Further, cleaning devices 10 are typically mounted such that adjacent cleaning devices 10 have alternate keyways 26(a) and 26(b) in contact with key 30. If one cleaning device 10 is placed on rotatable shaft 24 incorrectly, several cleaning devices 10 might have to be removed from rotatable shaft 24 to correct the alignment of cleaning device 10.
Existing cleaning devices 10 used for cleaning workpieces are often made by growing sponge-like material 12 on core 14. Core 14 is typically made of poly vinyl chloride. Core 14 is stamp cut, cleaned, and aligned within the mold. Typically, core 14 is suspended in a mold by alignment spacers while sponge resin is poured into the mold to surround core 14. The mold containing the sponge resin is then shaken to reduce the amount of gas entrapped in the sponge resin. The sponge resin is then baked until it solidifies into a sponge-like material, ideally forming a single sponge surrounding the core. The sponge-like material is then trimmed.
Using this process, core 14 may be inadvertently displaced when the mold is shaken; inadvertent displacement of core 14 within the mold may result in uneven and unpredictable growth of sponge-like material 12 on core 14. If more sponge-like material is on one planar side of core 14, unequal pressure will be applied between the workpiece and cleaning device 10, resulting in unpredictable cleaning of the workpiece. Other manufacturing defects encountered with this process include: sponge-like material 12 not sealing over outer edge 20 of core 14, too many air bubbles in sponge-like material 12, and not enough sponge-like material 12 at the inner portion of core 14. Moreover, the stamping, shaking, and trimming steps are time consuming and labor intensive; these steps may unnecessarily increase the manufacturing cost of cleaning devices 10.